Investors & landlords

I have a client that is renting to a pastor and renting below FMV, the client is wondering if the difference can be written off as a donation?  This is on a fiduciary tax return.  Also, this client is wondering if the donation can be used as a tax credit to help offset his father's tax debt.  The father passed away 3 years ago, so I don't know if this is pertinent or not.